The primary objective of this study is to determine the effects of clarithromycin on the cytochrome P450 enzymes 1A1/2, 2D6, 3A4 and 2C8/9 using caffeine, dextromethorphan, tolbutamide and their metabolic products as markers. In the first phase, patients will first have their metabolic markers and their metabolic products measured. The patients will then take a course of at least seven days of clarithromycin to initiation of the second phase. The metabolic markers will be readministered and they and their metabolic products measured. The serum and rine samples collected from volunteers will be analyzed by high pressure liquid chromatography.